The present invention relates to method and/or apparatus for measuring an intake air quantity of an internal combustion engine, and more specifically to intake air quantity measurement for an engine of a type capable of continuously varying intake valve lift and intake valve timing in accordance with engine operating conditions.
Published Japanese Patent Application KOKAI Numbers H9-303242; and H11-117777 show engines of a type for regulating the intake air quantity mainly by altering an intake valve lift characteristic.
In a gasoline engine, an intake negative pressure or intake vacuum produced by a throttling operation of a throttle valve to restrain load is liable to increase pumping loss (throttle loss) and hence to deteriorate the thermal efficiency and fuel consumption in light load region, as compared to a diesel engine having no throttle valve. This problem can be met by the technique of regulating the intake air quantity by varying the intake valve lift characteristic. When an air flowmeter is needed, however, the addition of the air flowmeter tends to complicate the construction and increase the cost. Moreover, the measurement of intake air quantity is more or less inaccurate due to back flow formed near the air flowmeter in the intake passage by intake pressure fluctuation. By increasing the volume of a collector section on the upstream side of the intake ports of engine cylinders, it is possible to reduce the intake pressure amplitude and restrain the back flow near the air flowmeter. In this case, however, the volume increase of the collector section increases a time from an actual change in the intake air quantity caused by a change in the valve lift characteristic, to a reflective change in the measurement of the air flowmeter. As a result, the measurement of the intake air quantity tends to be less accurate in such a transient state, and the control of the fuel injection quantity and air-fuel ratio based on the intake air quantity measurement tends to be less accurate.
It is an object of the present invention to provide method/system for measuring or controlling intake air quantity, specifically in a very light load engine operating region.
According to the present invention, an intake air quantity measuring method for an engine arranged to continuously control an intake air quantity by varying an intake valve operating characteristic, comprises: sensing an engine speed; sensing an intake valve lift; detecting a very light engine load region; and calculating an intake air quantity in accordance with the engine speed and the intake valve lift when the very light engine load region is detected.
According to the present invention, an intake air quantity measuring apparatus for an engine arranged to continuously control an intake air quantity by varying an intake valve operating characteristic, the intake air quantity measuring apparatus comprises: a first sensor to sense an engine speed; a second sensor to sense an intake valve lift; and a controller programmed to detect a very light engine load region; and to calculate an intake air quantity in accordance with the engine speed and the intake valve lift when the very light engine load region is detected.
According to another aspect of the present invention, an engine control system comprises: means for continuously controlling an intake air quantity of an engine by varying an intake valve operating characteristic; means for sensing an engine speed of the engine; means for sensing an intake valve lift of the engine; means for discriminating a very light engine load region from a remaining engine operating region; means for calculating an intake air quantity in a first control mode in the case of the remaining engine operating region; and means for calculating the intake air quantity in a second control mode in accordance with the engine speed and the intake valve lift in the case of the very light engine load region.